This invention relates to an input torque control system for a variable displacement pump, and while the invention is subject to a wide range of applications, a preferred embodiment of the invention will be particularly described as applied to input torque control of a cylindrical variable displacement pump.
Input torque control has the advantage of improved efficiency of a hydraulic system, particularly as it eliminates the corner horsepower requirement. It is known to provide input torque control for a pressure compensator in a hydraulic control system by causing a pressure compensator sleeve to be axially operable in accordance with mechanically linking the sleeve with a pump displacement control cam. This can be done so as to select desired characteristics by including in the linkage a selected conically shaped cam to vary the ratio of movement of the compensator sleeve as desired relative to the positioning of a pump displacement control cam. Systems of this nature are known, for example in the prior U.S. Pat. Nos. 3,669,570 and 3,985,469. In the U.S. Pat. No. 3,669,570, a compensator sleeve has a cam follower formed on one end thereof which selectively bears against one of two peripheral cam surfaces on a lever that is described as being subject to actuation in accordance with the positioning of a pump displacement control cam. One of the cam surfaces is shaped for defining a predetermined regulated level corresponding to a desired constant power output. The second cam surface is a pressure limit control. In order to select a different characteristic output of the pump, it would be necessary to substitute a lever having a different cam structure.
An object of the present invention is to provide an input torque system for a variable displacement pump which substantially obviates one or more of the limitations and disadvantages of the described prior art systems.
Another object of the present invention is to simplify input torque control systems for variable delivery pumps by providing an external adjustment for designating a desired pressure limit control for a pump.
Another object of the present invention is to improve the efficiency and reduce the cost of input torque control systems for variable displacement pumps.
Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part point out as the description of the invention progresses.